1. Field of the Invention
The present invention relates to an image recording method and an apparatus therefor, especially to a line-sequential recording method and an apparatus therefor, by which an image is recorded on a recording material in a line sequential fashion on the basis of image data of the image to record.
2. Background Arts
There are frame-simultaneous method, line-sequential method and dot-sequential method in image recording. In the frame-simultaneous method, an image frame is recorded on a recording material at one time. In the line-sequential recording method, an image frame is recorded line by line on a recording material. In the dot-sequential method, an image frame is divided into dots or pixels and is recorded one dot after another on a recording material.
Widely used silver-salt photo-printers adopt the frame-simultaneous method, wherein an optical image of an original recorded on a photo film is projected onto a photographic material such as a photographic paper through an image forming lens. On the other hand, widely used photo-copiers adopt the line-sequential method, wherein an original image is scanned by a light strip, and a light reflected from the original image is projected onto a rotating photosensitive drum, forming an electrostatic image on the drum. The electrostatic image is developed by depositing toner, and the toner-image is transferred to and fixed on ordinary paper. The dot-sequential method is usually used in ink jet printers, wherein a head ejects ink dots while moving in a main scan direction or the crosswise direction of the recording paper that is moving in a sub-scan direction perpendicular to the main scan direction. Thus the ink dots are sequentially disposed on the recording material to record an image frame.
Besides the above optical image recording apparatuses that optically form an image from an original, many types of digital image recording apparatuses have been developed. In the digital image recording apparatus, digital image data is transformed into an optical image through an image projection device, e.g., LCD, CRT, digital micromirror device (DMD), laser scanner, and electro-luminescent display. Besides light and ink, it is also known in the art to project electromagnetic rays, including X rays, ultraviolet rays, infrared rays, and electron beams, or powdery or liquid pigment onto a recording material on the basis of electric image signals, for recording an image or a latent image. Also in those recording apparatuses based on the electric image signal, the image is recorded according to the frames-imultaneous method, the line-sequential method or the dot-sequential method.
In order to achieve an adequate resolution, the digital image recording apparatus needs a high pixel density, i.e., an enormous number of pixels per frame. Accordingly, for the frame-simultaneous method, a very complicated and expensive image projection device is necessary. On the other hand, the dot-sequential method needs a main scanning mechanism and also takes a longer time compared to the other methods. For this reason, the line-sequential method has been preferred in the digital image recording apparatus, as it costs less than the frame-simultaneous method, and its printing speed is higher than that of the dot-sequential method, but lower than that of the frames-imultaneous method.
In the digital image recording apparatus adopting the line-sequential method, the image projection device is mounted stationary, while a recording sheet is transported at a constant speed in a sub-scan direction perpendicular to a main scan direction along which each line of the image to print extends. In many cases, transport rollers nip the recording sheet before and behind a recording stage to transport the recording sheet through the recording stage, while applying a certain tension to maintain the recording sheet flat in the recording stage.
Because of margins necessary for the transport rollers, it is impossible to use the entire area of the recording sheet for recording. In addition, the transport rollers may slip and make the transport unstable due to various surface conditions of the recording material. Instability in transport can cause unexpected variations in recording density, or lower the flatness of the recording sheet in the recording stage and thus lower the sharpness of the recorded image. Moreover, the gap between the transport rollers of each pair should be adjusted according to the thickness of the recording material.
In view of the foregoing, an object of the present invention is to provide a recording method which makes it possible to print a high quality image on the entire area of a recording material, and an apparatus therefor.
A second object of the present invention is to provide an image recording apparatus which is easy to adjust to the physical properties of the recording sheet such as thickness, frictional factor, and modules in tension, as well as to the size of the recording sheet.
Another object of the present invention is to provide a image recording apparatus which is inexpensive and simple in construction, and has small moving elements.
A further object of the present invention is to provide an image recording apparatus which can make the frame-simultaneous recording as well as the line-sequential recording.
To achieve the above and other objects, according to an image recording method of the present invention, a recording material is held stationary at a recording station, and electromagnetic rays or pigment is projected onto the recording material held stationary at the recording station for recording at least one line at a time along a main scan direction, projecting position of the electromagnetic rays or pigment onto the recording material being shifted in a sub-scan direction perpendicular to the main scan direction at a predetermined speed, to record an image frame line by line on the stationary recording material.
An image recording apparatus of the present invention is provided with a holding device for holding a recording material stationary at a recording station; a line image projection device for projecting electromagnetic rays or pigment onto the recording material for recording at least one line at a time along a main scan direction while the recording material is held stationary at the recording station; and a scanning device for shifting projecting position of the electromagnetic rays or pigment onto the recording material in a sub-scan direction perpendicular to the main scan direction at a predetermined speed, to record an image frame line by line on the stationary recording material.
Because it is unnecessary to transport the recording material during the recording of one frame, the recording apparatus of the present invention is free from the problems as described above.
According to a preferred embodiment, the holding device holds the recording material to be flat at the recording station by vacuum suction.
According to a preferred embodiment, the scanning device shifts the line image projection device in parallel to the sub-scan direction of the stationary recording material, to shift the projecting position of the electromagnetic rays or pigment onto the recording material.
According to another preferred embodiment, wherein the electromagnetic rays are recording light, and the recording material is a photosensitive material, the scanning device is comprised of a mirror for directing the recording light from the line image projection device toward the photosensitive material; and a mirror shift device for shifting the mirror along a light path of the recording light that is defined by the line image projection device and the projecting position of the recording light on the photosensitive material, the mirror shift device maintaining the mirror at a constant angle to the photosensitive material.
As it is only necessary to move a single small mirror, it is easy to combine a frame exposure device for recording an image frame at a time with the line-sequential exposure device of this embodiment.